The present disclosure relates generally to an arrangement for, and a method of, locating and tracking a mobile device that is movable in a venue by transmitting ultrasonic ranging signals in a time difference of arrival (TDOA)-based ultrasonic locationing system to an ultrasonic receiver on the mobile device, and, more particularly, to inferring transmit timer values of the ranging signals to simplify and expedite operation of the TDOA-based locationing system in accurately locating the mobile device.
It is known to deploy a real-time ultrasonic locationing system in a venue to locate and to track a mobile device that is movable in the venue. The known ultrasonic locationing system includes an ultrasonic transmitter subsystem having a plurality of ultrasonic transmitters mounted at fixed, known locations spaced apart in the venue, each ultrasonic transmitter being operative, in its turn, for periodically transmitting ultrasonic ranging signals, e.g., ultrasonic pulses in the 20-22 kHz frequency range, to an ultrasonic receiver subsystem having a receiver, e.g., a microphone, mounted on, and jointly movable with, the mobile device. The ultrasonic locationing system locates the position, and tracks the movement, of the mobile device along a tracking path within the venue, typically by using flight time measurements known in the art that incorporate triangulation, trilateration, multilateration, and like techniques.
One type of known flight time measurements employs time of arrival (TOA) or time of flight (TOF) techniques, in which the ranging signals are transmitted at known transmit timer values, and in which the ranging signals are received by the receiver at known receive timer values. The flight time difference between the known transmit timer values at which each ranging signal is transmitted and the known receive timer values at which each ranging signal is received, together with the known speed of each ranging signal, as well as with the known locations of the transmitters, are used, among other factors, such as temperature and humidity, to determine the distance from each transmitter to the receiver mounted on the mobile device, and, in turn, the location of the mobile device. Synchronization between the transmit timer values and the receive timer values is necessary in a TOA/TOF-based system.
Another type of known flight time measurements employs time difference of arrival (TDOA) techniques, in which the transmit timer values of the ranging signals transmitted by the transmitters are not known. The receive timer values of the ranging signals are known, but there is no synchronization between the transmit timer values and the receive timer values. More particularly, the ranging signals transmitted by a first pair of transmitters deployed at fixed, known locations in a TDOA-based locationing system are received by the receiver and generally indicate that the mobile device may be located at any one of a multitude of possible locations that may be plotted as a two-sheeted, first hyperboloid. The ranging signals transmitted by a third such transmitter and received by the receiver generally indicate that the mobile device may be located at any one of another multitude of possible locations that may be plotted as a second hyperboloid. When considered together, the mobile device may be located on the curve along which the first and second hyperboloids intersect. The ranging signals transmitted by a fourth such transmitter and received by the receiver generally indicate that the mobile device may be located at any one of still another multitude of possible locations that may be plotted as a third hyperboloid. When all are considered together, the mobile device may be located at one or two points, one for each of the two sheets of the first hyperboloid, where all the hyperboloids intersect. A fifth such transmitter may be needed to resolve the ambiguity between the two points unless one of the points can be excluded due to physical constraints, such as by being located above a ceiling of the venue.
Hence, the TDOA-based system generally requires more transmitters as compared to a TOA/TOF-based system. Finding the mobile device location from four TDOA measurements from five transmitters requires three homogeneous linear equations to be simultaneously solved, with concomitant tradeoffs on result certainty, accuracy, run time, and coding complexity. Although there are many robust linear algebraic methods, such as singular value decomposition or Gaussian elimination, which can solve for the three coordinates of the location of the mobile device, none of these methods are able to deliver a result having all of: high accuracy, high confidence, and fast answer determination. Rapidly determining the location of the mobile device by triangulation/trilateration/multilateration techniques in real time is critical, especially if the mobile device has moved while waiting for the TDOA-based system to complete its computations.
Accordingly, it would be desirable to reduce the number of transmitters in such TDOA-based locationing systems, to reduce the computational burden in such TDOA-based locationing systems, and to rapidly and accurately locate and track mobile devices in venues in which such TDOA-based locationing systems are deployed.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and locations of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The arrangement and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.